Semiconducting cadmium cadmium-zinc and mercury phosphide halides

ABSTRACT

Disclosed are phosphide halides of cadmium, cadmium-zinc, and mercury which are semiconductors and which may be doped with materials such as indium, copper, magnesium, and the like. The compositions are useful in semiconductor devices such as thermistors, rectifiers and visible light and infrared detectors.

United States Patent 1 Donohue [54] SEMICONDUCTING CADMIUM CADMIUM-ZINCAND MERCURY PHOSPHIDE HALIDES [75] Inventor: Paul ChristopherWilmington, Del.

[73] Assignee: E. I. du' Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Aug. 10, 1971 [21] Appl. No.: 170,622

Related US. Application Data [63] Continuation-impart of Ser. No.24,821, April 1,

1970, abandoned.

Donohue,

[52] US. Cl. ..252/5l8, 252/501, 23/368, 252/623 ZB, 338/18 [51] Int.Cl. ..H0lb 1/06, C0lg 11/00 [58] Field of Search ..252/50l, 518, 62.3 R,62.3 28; 23/367, 368; 338/18 [56] References Cited UNITED STATES PATENTSSuchow ..23/367 1 Apr. 3, 1973 OTHER PUBLICATIONS PrimaryExaminer-Charles E. Van Horn Attorney-Anthony P. Mentis [57] ABSTRACTDisclosed are phosphide halides of cadmium, cadmium-zinc, and mercurywhich are semiconductors and which may be doped with materials such asindium, copper, magnesium, and the like. The compositions are useful insemiconductor devices such as thermistors, rectifiers and visible lightand infrared detectors.

17 Claims, N0 Drawings SEMICONDUCTING CADMIUM CADMIUM-ZINC AND MERCURYPHOSPHIDE HALIDES CROSS REFERENCE TO RELATED APPLICATION y is -l .2 whenM is Cd and X is CI, but otherwise is This application is acontinuation-in-part of my It is to be understood that the subscript ofX is l and accopending application Ser. No. 24,821, filed Apr. 1, 1970and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to new cadmium, cadmiumzinc, and mercury phosphide halides.

2. Description of the Prior Art A number of phosphide halides,antimonide halides, and arsenide halides of cadmium and mercury havebeen reported previously. Semiconductive cadmium pnictide halides offormula Cd,,Y X in which Y is an element selected from Group V-A of thePeriodic Table and X is an element selected from Group VII-A of thePeriodic Table have been described by L. Suchow in US Pat. No.3,303,005. Compounds with cubic crystal structure and formula Cd (P,As),(Cl,Br,l) have been described by L. Suchow and N. R. Stemple in J.Electrochem. Soc. 110, 766 (1963). The cadmium arsenide halides Cd As ClCd AsCl Cd AsCl and Cd AsCl have been reported by H. Puff, et al. inNaturwissenschaften 52, 452 (1965) and in Z. Anorg. Allg. 343, 259(1966). Cadmium antimonide iodide, Cd Sb I has been reported by H. Puffand H. Gotta, Z. Anorg. Allg. Chem. 341, 324 (1965). Substancesformulated as P(CdCl) P(CdI) etc. have been reported by Y. I. Podinovand V. R. Klokman, Radiokhimiya 8, 556 (1966).

The mercury antimonide I-Ialides Hg Sb I I-Ig SbI HgSbBr, and HgSbBrhave been reported by H. Puff and H. Gotta in Z. Anorg. Allg. Chem.333, 280 (1964), 337, 157 (1965) and Naturwissenschaften 51, 535 (1964).S. Prasted and coworkers have reported HgzSbBr HgSbBr Hg SbCl andI-IgSbCl in the J. Indian Chem. Soc. 41, 771 (1964), 42,195(1965).

The mercury arsenide halides Hg AsCl Hg AsBr Hg As Cl and Hg As Cl havebeen reported by H. Puff, Angew. Chem. 74, 659 (1962). H. Puff, R.Skrabs, H. Gotta and P. Blunck, Naturwissenschaften S2, 494 (1965) havereported HgAsCl, Hg AsCl Hg AsBr Hg As Cl and Hg As I Reported mercuryphosphide halides include Hg PCl and Hg P Bn, [P. Lemoult, Compt. Rend.145, l 175 (1907)], Hg P I [D. Grdenic, S. Scavnicar, and M. Kesler,Arhiv. Za Kemiju 24, 61 (1952)], Hg P l, [I-I. Puff and P. Blunck, Z.Anorg. Allg. Chem. 349, 39 and Hg PCl HggpBrg, and Hgfg zclg Puff,Angew. Chem. 74, 659 (1962)].

No cadmium, cadmium-zinc or mercury phosphide halides having thestoichiometry M ,,Zn,,P X, where M is Cd or Hg, X is Cl, Br, or I, and yis 0-1.2 have been reported.

DESCRIPTION OF THE INVENTION This invention provides new electricallysemiconducting cadmium, cadmium-zinc, and mercury phosphide halideshaving the formula M ,,Zn,,P X, wherein:

M is selected from one of Cd and Hg,

X is selected from at least one member of the group consisting of Cl,Br, and I when M is Cd, and from cordingly that the sum of chlorine,bromine and iodine atoms in the formula never exceeds one.

The phosphide halides of the invention are semiconductors andphotoconductors, and their electrical and optical properties may bevaried by doping them with ions such as In, Cu, Ag, Mg, Mn, S Se, and Tein quantities ranging from a few parts per million to about one percentby weight, the exact quantity depending upon solubility relationshipsand properties desired.

The cadmium and the cadmium-zinc phosphide halides and the mercuryphosphide chloride of this invention are isostructural, with monocliniccrystal structure, and the space group C2/c. In contrast, mercuryphosphide bromide, Hg P Br, has an orthorhombic crystal structure andthe space group Pbcn.

Although Cd Zn P X compositions, where X and y are as defined, andHggPaCl have similar monoclinic crystal structures and space groups, thetwo do not appear to form solid solutions with each other, possiblybecause of differences in the covalency of bonding. In addition, thecadmium and the mercury compositions differ in acid stability. Thecadmium-containing compositions dissolve in strong acids whereas Hg P Cland Hg P Br are insoluble even in aqua regia.

At least 50 atomic percent of the CI in Hg P Cl may be replaced with Brwithout change in the monoclinic crystal structure of the Hg P Cl, butwith increase in unit cell dimensions. Similarly, at least 30 atomicpercent of the Br in Hg P Br may be replaced with Cl without change inthe orthorhombic crystal structure of the l-lg P Br, but with decreasein unit cell dimensions. Mercury phosphide bromide chlorides ofintermediate composition are polyphase and made up of materials withmonoclinic and orthorhombic crystal structures.

The cadmium and the cadmium-zinc phosphide halides are obtained byreactions of mixtures of the requisite elements and/or their binarycompounds preferably in the approximate ratios required for thestoichiometry Cd Zn P X, wherein X and y are as defined previously.Reaction is effected by heating the mixed reactants for several hours,e.g., for 3-48 hours, at temperatures of 500-900C, preferably inevacuated sealed tubes wherein there is maintained a temperaturegradient permitting vapor phase transport and crystallization of productin the cooler end. Pressure may range from essentially zero to 3,000atmospheres or more.

Mercury-containing compositions of the invention, like thecadmium-containing compositions, may be prepared by reaction of mixturesof the requisite elements and/or their binary compounds in, preferably,the approximate ratios required for the stoichiometry Hg P X, where X isselected from at least one of Cl and Br. Reaction is effected by heatingthe mixed reactants at about 400600C, preferably at 500C underautogenous pressure, for periods up to about 24 hours and then cooling,usually slowly over a period of about 10-40 hours to 200 300C, then atany convenient rate to room temperature.

Reaction is effected in the absence of air, conveniently in initiallyevacuated, sealed, thick-walled silica tubes. When sealed silicareaction tubes are used, they are usually heated in. a vessel pressuredto about 100-200 atmospheres with nitrogen. The nitrogen pressurecounterbalances any vapor pressure of mercury developed during reactionand prevents rupture of the reaction tube from internally developedpressure. In synthesizing l-lg P Cl it seems necessary to use a largequantity of reactants in a reaction tube of fairly small volume, viz.,about 20 grams in a tube of about 8 ml. capacity see Examples 14 and 20.Presumably a pressure slightly higher than a few atmospheres is needed.This is not required in the preparation of l-lg P Br. Reaction tubes arepreferably horizontally disposed during reaction to prevent localizedsettling of mercury vapor and its ensuing unavailability for reaction.The same result may be achieved by agitating during reaction.

Typical reactions involved in preparing compositions of the inventionare:

ln equations 7, l4, and 15, y is -1.2. ln equations and 13, X isselected from at least one of the group consisting of Cl, Br, and l.

Extremely pure reactants are not required. Commercially available gradesusually give satisfactory results though purer reactants, in general,give products of higher purity. Binary compounds especially useful insynthesizing cadmium and cadmium-zinc phosphide halides include thephosphides and halides of cadmium and zinc and the halides ofphosphorus, notably CdP CdP Cd P ZnP CdX ZnCl PX and PX Binary compoundsespecially useful in synthesizing mercury phosphide chloride and mercuryphosphide bromide include mercury (I), mercury (II), phosphorus (III)and phosphorus (V) halides. Since elementary chlorine and bromine arevolatile, it is usually more convenient to employ their compounds ratherthan the free halogens.

Though reactants are usually employed in the stoichiometric ratiorequired for the final coi'npositions, this is not essential. Excessreactants, like impurities such as P, Hg, CdP CdX ZnP and PX which aresometimes found in the products, may usually be separated manually, byextracting with appropriate solvents, by flotation, or by other knowntechniques. Since the mercury phosphide halides, Hg P Cl and l-lg P Br,are insoluble and stable in strong acids, they may be freed of excessmercury, phosphorus halides,

and elementary phosphorus by washing them with aqua regia.

Nonstoichiometric inorganic compounds are well recognized (see, forexample, the Wadsley chapter in Mandelcorn, Non-stoichiometricCompounds", Academic Press, New York, 1964, pp. 98-209), and,accordingly, applicant intends that phosphide halides of the inventionwhich agree approximately with the stoichiometric formulas presentedherein are to be included within the scope of the appended claims.

Products of the invention may contain dopants to change the number andtype of the charge carriers, e.g., to lower activation energy andelectrical resistivity. Elementary forms of dopant metals may be addedduring synthesis to replace small quantities of cadmium or mercury, andsulfur, selenium, or tellurium may be added to replace limitedquantities of phosphorus. Dopants may also be added in the form of theirphosphides or halides with commensurate reduction in the quantity ofphosphorus and/or halide reactant normally employed.

The quantity of dopant added is determined primarily by its solubilityin products of the invention and by the properties desired. The quantityincorporated in the crystal lattice may sometimes be increased by rapidcooling after reaction to prevent segregation of dopant. Divalent metalsusually enter the crystal lattice in larger quantity than monovalent ortrivalent metal dopants.

Products of the invention are conveniently synthesized in tubular silicaor Pyrex reaction vessels which are readily available, relatively low incost, easily sealed, and chemically inert. Reactants are placed in thetubes which are then evacuated and sealed. Tubular reaction vessels areespecially useful in the synthesis of cadmium and cadmium-zinc phosphidehalides, for in these cases it is preferred to supply heat in suchmanner that the end of the tube containing the reactants in hotter thanthe other end. In both the cadmium and the mercury systems, horizontaldisposal of the reaction tubes is preferred.

The temperature gradient preferred during the synthesis of cadmium andcadmium-zinc phosphide halides is achieved most easily by placing theend of the tube containing the reactants in the hotter, central portionof a furnace with the other end of the tube near the open end of thefurnace. Furnaces equipped with independently controlled temperaturezones may also be used.

Usually with a temperature of about 500900C, preferably 550750C in thehotter end and about l50-350C in the cooler end, vapor transport takesplace in cadmium-containing synthesis systems, and cadmium-containingproducts of the invention, sometimes accompanied by by-products, form inthe cooler end. As shown in Example 5, more than one product of theinvention may deposit in the cooler end simultaneously, in which casesthe products may be separated manually.'0ccasionally, as illustrated inExamples 8 and 9, products of the invention form at both ends of thereaction tube.

While his preferred on grounds of economy and convenience to effectsynthesis in vacuo or at moderate pressure, pressures up .to 3,000atmospheres or more may be used. In such case thereactants may be sealedin evacuated heavy-walled Pyrex tubes which are placed in electricallyheated metal vessels in which pressure may be generated by applicationofv nitrogen or other gas- A pressure of up to about 200 atmospheres isapplied, and the temperature is raised to about 700C, whereupon thePyrex tubes soften and transmit subsequently applied pressure to thereaction mixtures. Desired temperature and pressure are maintained forabout three hours or more while reaction takes place. Pressure-isusually maintained during cooling. Cooling may be rapid if the pressurevessel is suitablyequipped.

.The-time required for reaction is not especially critical and, -asmight be expected, depends upon temperature'and pressure. In sealed,evacuated tubes, with. the

' hot end at about 500-900C, reaction and transport of product(s) isusually complete in 2448 hours or less. At 3000 atmospheres pressure,reaction may be complete in three hours or less.

' In sealed, evacuated. tubes in which temperature gradients aremaintained, Cd, ,,'Zn,,P X compositions,

' sometimes accompanied by by-products, usually form in the cooler endof the tubes as polycrystalline masses or -films, frequently containingsingle crystals up to Composi-' tion, a(A) I b(A) c( B Cd,P Cl7.9885:0.0006 8.9.878i0.0006 7.5552:0.0006 l00.9 Cd;P,Br 89892200019.089 $0.001 7.535 10.001 l00.4 ,cdgrn -8.244i0.00l 9.293 10.00l 7.50510.00] 99b6g$ 8.849 1000i 7.593 i0.00l 98.63

Mercury phosphide bromide, l-lgJgBr, has an orthorhombic space latticewith space group Pbcn and cell dimensions ofi a 8.014A., b 8.901A., andc 7.822A.- 1 i In contrast to known Cd P,X, compounds, which teristicsof the phosphide halides of this invention make them useful in a varietyof applications. All are semiconductors. For example, electricalresistivities and activation energies found for compositions describedin the examples were:

It will be noted that the resistivity of compositions intermediatebetween l-Ig P Br and Hg P CI is markedly lower than that of theendmembers. The compositions of the invention may be used insemiconductor devices such as thermistors, thermoelectrics, rectifiers,and detectors for visible and infrared light. 1

Cd P Cl is more photoconductive than the corresponding bromide oriodide, and Hg P Cl is more photoconductive than I-Ig P Br:

Ratio of Resistance in Dark to Resistance in Light Cd,P,Cl V Cd,P,Br 1.5Cd,P,l -5 Hg,P,Cl Hg,P,Br 40 Cadmium phosphide chloride, Cd P Cl, isthermochromic, changing from light orange at 77K to black at 573K. Thiseffect is useful in modulating the wavelength of transmitted light sincethe wavelength of transmitted light is a function of the temperature ofthe therrnochromic material. Thus, when thetemperature of thethermochromic material is varied in known manner, e.g., by simpleelectrical heating and cooling by contact with a thermoelectric elementwhich cools when current is passed in one direction and heats whencurrentis passed inthe other direction, the wavelength of transmittedlight is reproducibly changed as the current is altered in magnitudev ordirection.

SPECIFIC EMBODIMENTS OF THE INVENTION The following nonlimitativeexamples describe the practice of the invention. All parts are by weightunless otherwise indicated.

. EXAMPLES l 10 Reactions summarized in Table I were carried out insilica tubes which were evacuated and sealed after placing the indicatedquantities of reactants therein. The tubes were approximately 7 to 8inches in length with an internal diameter of about 10 mm and werehorizontally disposed in an electric furnace in such manner that the endcontaining the reactants was heated to a higher temperature than theother end, thus permitting vapor phase transfer and deposition ofproduct in the cooler end. The time of heating was approximately 48hours. Impurities and multiphase products were separated manually.

TABLE I Examples 1-10 Temperature, Reactants I Hot Cooler Formula ratioin which used end end Identity of product(s) .124 g. Cd, 0.16 ml. PO13,0.46% 2. P.. 340 C(12P3Cl (1) 24 g. Cd, 0.17 ml. PBra, 2331' (2)Quantity used FOOTNOTES FOR TABLE I (l) The product formed as redpolycrystalline film and large single crystals in the cooler end of thetube along with P, black crystalline Cd? and clear crystals of CdCl,.The P, CdP and CdCl, were separated manually. The Debye-Scherrer x-raypattern of the product is given in Table II. Anal. Calcd. for CdJ Cl:Cd, 63.65; P, 26.30, Cl, 10.04. Found: Cd, 62.7; P, 26.16; Cl, 10.34.Density by displacement in bromoform was 4.31 g/cm compared to 4.46 glcmcalculated for four formula units of Cd,P;,Cl per unit cell. The spacegroup was C2lc. Crystal structure by single crystal technique confirmedthe composition. Resistivity measurements on a crystal showedsemiconductivity: 298K 4 X 10 ohm-cm, activation energy, E, 0.6 eV.Ratio of resistance in the dark to resistance in light was 70. Theproduct reacted with concentrated hydrochloric acid, evolving a gas andforming an orange, flaky amorphous material that, by analysis, consistedpricipally of phosphorus.

(2) The charge was completely transported to the cooler zone andconsisted of polycrystalline brownish-red Cd,P Br plus traces of orangematerial which were separated manually. Guinier camera data were indexedon the basis of a cell analogous to that of Cd P CI but larger in size.Debye-Scherrer x-ray data are reported in Table ill.

(3) Charge was completely transported to cooler end and consistedprincipally of reddish-brown crystals which gave a Debye-Scherrer xraypattern similar to the product of Example 2. Anal. Calcd. for Cd,P,Br:Cd, 56.51; P, 23.36; Br, 20.13. Found: Cd, 56.11; P, 22.80; Br, 20.65.Resistivity and activation energy measured on a single crystalwere,p298K.. l0" ohm-cm; E, 0.7 eV; ratio resistance in the dark toresistance in visible light 1.5.

(4) Charge was completely transported to cooler end and consisted of atop layer of Cd? and a lower layer of Cd,P,l. The Debye-Scherrer patternof the Cd P l (see Table lV) resembled that of Cd P Cl and Cd,P,Br butwas shifted to a larger cell. Resistivity measurements on a polycrstalline chip showed p298l(.=l0 ohm-cm, E, =0.2 eV, and a small egree ofphotoconductivity (ratio of R IR S (5) Entire charge was transported tothe cooler end, giving a mixture of black Cd-substituted ZnP plus orangeand red crystals that gave X'-ray patterns of Cd,P,Cl-type but with cellsizes shifted in a manner that indicated Zn substitution in the crystallattice. The cell volume of the orange crystals was 506.7A. as comparedto 532.6A. for Cd,P,Cl; analysis by atomic absorption spectroscopyindicated formula to be Cd Zn hCl. Analysis by atomic absorptionspectroscopy indicated that the formula of the red material was cd Zn PCl; its cell volume was 5253A.

(6) Large dark-red crystals deposited in the cooler end were shown byunit eel dimensions to be a quaternary compound. Unit cell volume was540A. On the basis of Vegards rule, the cell dimensions corresponded toCd,P,Cl l.,

(7) Reddish crystals deposited in the cooler zone. The crystals gave asingle-phase x-ray diffraction pattern with cell dimensions intermediatebetween those of Cd,P Cl and Cd PgBr, thus indicating formation of aquaternary phase. Unit cell volume was 537.8A., which on the basis ofVegard's rule and cell dimensions corresponded to a formula of Cd,PCla0.58Br

(9) Part of the charge remained in the hot zone and part wastransported. Products in both ends were single-phase. X-ray diffractionpatterns and cell volumes corresponded to materials of Cd,P,Cl-type.that is, to S-element crystals corresponding to Cdl,Cl,,Br,,l, wherewhere a +b c i. Reactants were used in the proper ratio to giveCd,P;.,Cl,, Br l Cell volumes were 5417A." and 542.09AP, respectively,for materials from the hot zone and the cooler zone.

(10) Almost the entire charge was transported to cooler end of reactiontube as black crystals of ZnP and red crystals of Cd P Cl crystaltypewith, however, a smaller cell. Analysis by atomic absorptionspectroscopy showed 3.0% Zn and 62.4% Cd which corresponds to thecomposition Cd Zn P;,Cl.

TABLE 11 Debye-Scherrer X-Ray Pattern of Powder of Cd P Cl ilmlm of Ex.1

d(obs) TABLE I11 d(calc) Debye-Scherrer X-Ray Pattern of Powder of C d PBr of Ex. 2.

d(calc) TABLE IV Debye-Scherrer X-Ray Pattern of Powder of Cd P 1 of Ex.4.

1 h K I d(obs) d(calc) 55 2 2 1 2.70787 2.70384 2 1 0 3 2.47176 2.4732410 0 3 2 2.39455 2.39245 20 3 1 1 2.31882 2.31746 5 1 0 3 2.250422.24857 10 3 2 2 2.12053 2.11495 20 2 2 3 2.04814 2.05049 20 2 4 02.03221 2.03242 5 3 0 3 1.98808 1.98761 20 3 l 2 1.96728 1.96724 10 0 33 1.93114 1.93727 15 2 4 1 1.92247 1.91787 10 -4 0 2 1.90596 1.90500 5 40 1 1.85521 1.85980 10 l 3 3 1.82990 1.82850 10 0 1 4 1.81458 1.81120 101 5 2 1.66810 1.66926 5 2 5 1 1.63694 1.63696 2 5 l 1 1.60438 1.60466 153 4 2 1.53046 1.52988 5 4 4 2 1.48236 1.48141 5 2 2 5 1.40421 1.40228 23 6 1 1.35406 1.35346 5 0 5 4 1.31810 1.31875 5 1 0 6 1.24858 1.24830 52 0 6 1.23652 1.23662 unit cell defined by Miller indices are given inAngstroms.

EXAMPLE 1 1 This example illustrates the preparation of Cd P Br at highpressure. A mixture of 1.124 g. of cadmium, 0.16 ml. of PBr and 0.4646g. of phosphorus was ground together and sealed in 10 mm. outsidediameter by 6 mm. inside diameter Pyrex tubing. The tube and contentswere cold-pressured to 200 atmospheres with argon and heated to 700C., atemperature at which the Pyrex tube softened sufficiently to transmitpressure, further pressured to 3,000 atmospheres with argon, held at700C./3,000 atm. for hours, then cooled to room temperature in 2 to 3hours. The homogeneous, purplish, microcrystalline product' gave aDebye- Scherrer pattern identical to that reported in Table III for Cd PBr.

EXAMPLE 12 This example illustrates the preparation of indiumdopedcadmium phosphide chloride. A mixture of 1.011 g. cadmium, 0.115 g.indium, 0.16 ml. phosphorus trichloride, and 0.4646 g. phosphorus wassealed in vacuo in a silica tube. The tube was heated in a surroundingelectric furnace for 48 hours with the end containing the reactants at600C. and the other end at 300C. Material transported to the cooler endconsisted principally of a red crystalline phase. This red phase gave aDebye-ScherrerX-ray diffraction pattern of Cd P Cl-type with, however,slight shifting of cell constants indicating substitution of indium inthe cell lattice. This was confirmed by the resistivity and activationenergy of a crystal of the material:

Activation p298K. in Ohm-Cm. Energy in eV Undoped CdJ Cl 4 X 0.6

Indium-doped Cd,P,Cl 3 X 10 0.3

EXAMPLE 13 This example illustrates the doping of Cd P Cl with copper. Amixture of 1.0116 g. cadmium, 0.0633 g. copper, 0.16 ml. phosphorustrichloride, and 0.4646 g. phosphorus was sealed in vacuo in a silicatube and heated in a tube furnace for about 48 hours with the end of thetube containing the reactants at 700C. and the other end of the tube at300C. Red crystalline copper-doped cadmium phosphide chloride thatformed in the cooler region of the tube gave a Debye- Scherrer X-raydiffraction pattern similar to that of Cd P Cl but, as a result of thedoping with copper, the somewhat different resistivity and activationenergy of p298K. 10 ohm-cm. and E 0.5 eV respectively.

EXAMPLE l4 Hg P CI was obtained in an experiment in which a mixture ofHgCl 18.7531 g), P 1.2181 g), and Ge (0.0288 g) was sealed in vacuo in athick-walled (2 mm) silica tube of about 8 ml capacity and heated for 2hours at 500C. in a metal vessel pressured to 150 atmospheres withnitrogen to prevent rupture of the silica tube. Temperature was thenlowered to 300C. over a 40-hour period and finally to room temperature.The multi-phase product was washed with aqua regia leaving, among otherphases, black shining crystals found by analysis and x-ray methods to bel-lg P Cl. Calcd.: Cl, 6.69; P, 17.54. Found: Cl, 6.69; P, 17.11.Germanium was not detected by emission spectroscopy sensitive to 2 ppm.Cell dimensions and space group were determined by Buerger precessioncamera technique. Crystal structure was monoclinic and similar to thatof Cd P Cl. Cell dimensions were: a 7.840A., b 8.849A., c 7.593A., B98.63. The space group was C2/c. The crystals were semiconducting, witha resistivity, p, of 6.89 X 10 ohm-cm, and photoconducting with a ratioof resistance in the dark to that in light of 125. The Debye-Scherrerpowder diffraction pattern of the Hg P C1 is reported in Table V.

TABLEV X-RAY POWDER DIFFRACTION PATTERN OF Hg P Cl I h k 1 4(6b5)d(calc) 1 1 1 4.8754 4.8793 80 1 1 1 4.3693 4.3719 85 2 0 0 3.87483.8756 90 0 2 1 3.8125 3.8115 75 0 0 2 3.7522 3.7535 70 1 1 2 3.33163.3319 100 1 1 2 3.0057 3.0054 2 0 2 2.9237 2.9245 45 0 2 2 2.86212.8622 100 2 2 1 2.8288 2.8274 10 1 3 0 2.7564 2.7566 30 *1 3 1 2.63142.6336 85 2 2 1 2.6198 2.6196 10 1 3 1 2.5438 2.5441 10 2 0 2 2.51442.5142 5 3 1 0 2.4798 2.4801 5 3 1 1 2.4629 2.4630 85 1 1 3 2.40002.3998 80 1 3 2 2.2809 2.2806 65 3 1 1 2.2598 2.2600 95 0 4 0 2.21162.2121 1 3 2 2.1678 2.1673 10 0 4 1 2.1223 2.1219 3s 2 2 3 2.0146 2.014560 3 1 2 1.9442 1.9444 50 4 0 0 1.9379 1.9378 2 4 0 1.9214 1.9212 1 3 31.9048 1.9041 60 1 1 4 1.8486 1.8483 75 4 0 2 1.8380 1.8379 65 3 3 11.8319 1.8319 50 2 4 1 1.8296 1.8288 40 3 3 2 1.8116 1.8114 30 1 3 31.8058 1.8055 65 r 4 2 1 1.7833 1.7831 20 4 2 0 1.7753 1.7750 55 2 4 21.7646 1.7642 20 1 1 4 1.7306 1.7304 10 1 5 0 1.7257 1.7253 20 1 5 11.6941 1.6938 10 4 2 1 1.6767 1.6765 25 1 5 1 1.6695 1.6693 45 3 3 21.6516 1.6514 30 3 1 v 3 1.6472 1.6469 3 3 3 1.6264 151.6264 50 -3 1 41.6127 1.6125 30 2 0 4 1.5977 1.5977 45 1 3 4 1.5915 1.5913 10 2 4 31.5818 1.5817 20 4 2 3 1.5520 1.5519 20 1 5 2 1.5485 1.5481

EXAMPLE 15 This example illustrates the preparation of Hg P Br. Amixture of mercury (1.2179 g, 0.00607 g atom), mercuric bromide (0.7249g, 0.002011 mole), and phosphorus (0.3761 g, 0.01214 g atom) was sealedin vacuo in a heavy-walled silica tube, placed in a pressure vessel towhich 200 atmospheres back-up nitrogen pressure was applied, and heatedto 500C. Temperature was then gradually lowered to 300C over a 30- hourperiod and finally to room temperature. The product consistedprincipally of black, intergrown crystalline filmlike material and asmall amount of mercury. The mercury was extracted with aqua regia. Theundissolved material corresponded to Hg P Br in analysis. Calcd. for HgP Br: Br, 13.92; P, 16.18. Found: Br, 13.25; P. 17.22. ItsDebye-Scherrer x-ray pattern is reported in Table VI. By Buergerprecession camera technique, the crystal structure of the Hg P Br wasorthorhombic with space group Pbcn and cell constants of a 8.014A., b8.901A., and c 7822A. It was semiconducting with a resistivity of 6 X10" ohm-cm, and an activation energy, E of 0.67 eV. The compositionwas'photoconductive with a ratio of resistance in the dark to that inlight of 40.

TABLE VI X-RAY POWDER DIFFRACTION PATTERN OF Hg p Bl l h k I tobl)hrfllt) 20 l 1 5.9493 5.9556 10 1 l l 4.7344 4.7384 70 0 2 0 4.44884.4504 80 2 0 0 4.0056 4.0069 45 0 2 1 3.8663 3.8681 95 l 0 2 3.51513.5147 95 1 2 l 3.4839 3.4835 70 2 l 1 3.3096 3.3104 40 l l 2 3.26813.2690 75 2 2 0 2.9773 2.9778 80 2 0 2.7980 2.7987

95 l 2 2 2.7584 2.7582 65 2 l 2 2.6698 2.6699 25 l 3 1 2.6213 2.6214 603 l l 2.4314 2.4317 35 l l 3 2.3882 2.3884 15 2 2 2 2.3691 2.3692 95 0 23 2.2496 2.2496 90 3 0 2 2.2060 2.2058 75 3 2 l 2.11982 2.1980 60 l 2 32.1659 2.1659 60 0 4 l 2.1405 2.1402 3 l 2 2.1410

1 0 4 1.8997 55 4 l l 1.8964 1.8962 60 2 4 l 1.8878 1.8878 50 l 4 21.8802 1.8801 60 4 2 0 1.8267 1.8268

EXAMPLE 16 A composition with formula of Hg P Br cl was prepared bysealing a mixture of HgCl (1.0572 g), HgBr, (0.4036 g). Hg (1.1230 g),and P (0.4162 g) in vacuo in a heavy-walled silica tube and heating in apressure vessel under 100 atmospheres back-up nitrogen pressure for 12hours at 450C, then slowly cooling over a 12-hour period to 200C, andfinally to room temperature. The product consisted principally of blackcrystals from which other phases were extracted by treatment with aquaregia. Data obtained by chemical analysis corresponded to a formula of Hg P Br0.5Cl0 Calcd: P, 16.84; Br, 7.25; Cl, 3.21. Found: P, 16.34; Br,7.07; Cl, 3.48. The x-ray powder pattern showed that the crystals had amonoclinic Hg P Cl-type structure with dimensions shifted in thedirection of larger cell size, i.e., with a 7.881A., b 8.907 A., c=7.603A., B 98.37, and V 5286A".

EXAMPLE 17 A material of orthorhombic Hg P Br-t'ype structure withcomposition approximating Hg P Br Cl was obtained by reaction of HgBrHgCl, Hg, and P in quantities equivalent to 2:3:0.7:0.3 formula weightratio of HgzPzBrzCl. The mixture of 0.3375 g (0.000936 mole) of HgBr0.1895 g (0.00803 mole) of HgCl, 0.7245 g (0.003612 g atom) of Hg and0.2485 g (0.008024 g atom) of P, was sealed in vacuo in a heavywalledsilica tube and heated in a metal pressure vessel at 500C. for 10 hours(100 atmospheres back-up pressure). The tube was cooled to 300C. over a10-hour period and then to room temperature. The product consistedlargely of black shiny crystals and was separated from excess Hg bywashing with aqua regia.

. The X-ray diffraction powder pattern was of orthorhombic Hg l Br-typewith a 7.978A., b 8.862A., C 7.799A., and V 551.4A. The product had aresistivity at 298K of 8 ohm-cm and an activation energy, E of0.22 eV.

EXAMPLE 18 This example illustrates the preparation of a materialapproximating Hg P Br cl in composition by reaction of HgBr HgCl, Hg,and P in 2:3:0.9:0.1 formula weight ratio of Hg:P:Br:Cl. A mixture ofI-lgBr (0.4271 g, 0.001185 mole), HgCl (0.0622 g, 0.000263 mole), Hg(0.765 g, 0.003818 g atom), and P (0.2447 g, 0.007901 g atom) was sealedin vacuo in a heavywalled silica tube and reacted, cooled, and washed asdescribed in Example 17. The X-ray diffraction powder pattern showedthat the crystals had the orthorhombic Hg P Br-type structure. Cellconstants were: A 7.975A, B 8.871A, C 7.813A', and V 552.7A Theresistivity, p298K, was 1 X 10 ohm-cm.

EXAMPLE l9 Mercuric bromide (0.4709 g, 0.001307 mole), mercury (0.7863g, 0.00392 g atom), and phorphorus (0.2428 g, 0.00784 g atom) weresealed in vacuo in a heavy walled silica tube (wall thickness of 2 mm).The tube was placed in a horizontal pressure vessel, pressured withatmospheres of nitrogen back-up pressure, and heated at 500C for 10hours. Temperature was then gradually lowered to 300C over a 10-hourperiod and finally to room temperature. The product consisted almostentirely of black crystals. Impurities were extracted with nitric acid.The purified product was judged to be Hg P Br by its x-ray diffractionpowder pattern, and this was confirmed by analysis. Calcd. for Hg P BrzHg, 69.89; P, 16.19; Br, 13.92. Found: Hg, 70.1; P, 16.8; Br, 13.5.Density: found, 6.812 g/cm; calcd. for 4Hg P Br/cell, 6.822 g/cm. Byemission spectrography, impurities were: B, 100-500 ppm; Cu, 50-250 ppm;Mg, Mn, 2-10 ppm; and Si,Fe, 1-5 ppm. The boron and copper may beconsidered as doping elements.

EXAMPLE 20 A mixture of HgCl (8.9146 g, 0.0378 mol), Hg

- (7.5757 g, 0.0378 g atom), and P (3.5094 g, 0.1133 g atom) was sealedin vacuo in a silica tube approximately cm in length by 15 mm outsidediameter. The tube had a wall thickness of about 2.5 mm and a measuredcapacity of about 8 ml. The tube and contents were heated for 10 hoursin a horizontal position in a pressure vessel at 500C. using 150atmospheres backup pressure, then gradually cooled over a -hour periodto 300C. and, finally, rapidly to room temperature. The tube contained,principally, black shiny crystals of Hg P Cl with some excess Hg, PCland P. The impurities were extracted with nitric acid, leaving Hg P Clwhich was identified by its x-ray diffraction powder pattern.

EXAMPLE A As shown by the photoconductive response to visible light ofthe Cd P Cl of Example 1, the Cd P Br of Example 3, the Cd P l ofExample 4, the cd p ci g of Example 6, the indiumand copper-doped Cd PCl of Examples 12 and 13, and the compositions of examples l4 and 15,some of the phosphide halides of the invention may be used to detect andmeasure the intensity of visible light. This may be accomplished byconnecting crystals of compacts (highly compacted masses in the form ofbars or pellets, etc.) of the products in series in an electricalcircuit comprising (1) a source of current,

l. A semiconducting phosphide halide of the formula M Zn P X wherein Mis Cd or Hg;

X is at least one member of the group Br, Cl and 1 when M is Cd; and atleast one member of. the group Br and Cl when M is Hg;

y is 0 to 1.2 when M is Cd and X is Cl, but otherwise 2. A compositionof claim 1 containing a small amount of a dopant selected from the groupconsisting of In, Cu ,Ag Mg, Mn, 8", Se and Te 3. A composition of claim1 in which M is Cd.

4. A composition of claim 1 in which M is Hg.

5. The composition of claim 3 in which y 0 and X is chlorine; Cd P Cl.

6. The composition of claim 3 in which y 0 and X is bromine; Cd P Br.

7. The composition of claim 3 in which y 0 and X is iodine; cd P l.

8. The composition of claim 3 in which y 1.16 and X is chlorine; Cd Zn PCl.

9. The composition of claim 3 in which y 0.46 and X is chlorine; Cd Zn PCl.

10. The composition 0 c aim 3m Wl'llCh y 0.16 and 11. The composition ofclaim 3 in which y 0 and X is 0.74 chlorine and 0.26 iodine; Cd P Cl I12. The composition of claim 3 in which y 0 and X is 0.58 chlorine and0.42 bromine; Cd P Cl Br 13. The composition of claim 3 in which y 0 andX is 0.59 bromine and 0.41 iodine; cd P Br l 14. The composition ofclaim 3 in which y 0 and X- is 0.83 bromine and 0.17 iodine; Cd P Br l15. The composition of claim 4 in which y 0 and X is Cl; Hg P Cl.

16. The composition of claim 4 in which y 0 and X Br; Hg P Br.

17. The composition of claim 4 in which y 0 and X is 0.5 Br and 0.5 CI;Hg P Br Cl

2. A composition of claim 1 containing a small amount of a dopantselected from the group consisting of In3 , Cu1 , Ag1 , Mg2 , Mn2 , S2 ,Se2 , and Te2 .
 3. A composition of claim 1 in which M is Cd.
 4. Acomposition of claim 1 in which M is Hg.
 5. The composition of claim 3in which y 0 and X is chlorine; Cd2P3Cl.
 6. The composition of claim 3in which y 0 and X is bromine; Cd2P3Br.
 7. The composition of claim 3 inwhich y 0 and X is iodine; Cd2P3I.
 8. The composition of claim 3 inwhich y 1.16 and X is chlorine; Cd0.84Zn1.16P3Cl.
 9. The composition ofclaim 3 in which y 0.46 and X is chlorine; Cd1.54Zn0.46P3Cl.
 10. Thecomposition of claim 3 in which y 0.16 and X is chlorine;Cd1.84Zn0.16P3Cl.
 11. The composition of claim 3 in which y 0 and X is0.74 chlorine and 0.26 iodine; Cd2P3Cl0.74I0.26.
 12. The composition ofclaim 3 in which y 0 and X is 0.58 chlorine and 0.42 bromine;Cd2P3Cl0.58Br0.42.
 13. The composition of claim 3 in which y 0 and X is0.59 bromine and 0.41 iodine; Cd2P3Br0.59I0.41.
 14. The composition ofclaim 3 in which y 0 and X is 0.83 bromine and 0.17 iodine;Cd2P3Br0.83I0.17.
 15. The composition of claim 4 in which y 0 and X isCl; Hg2P3Cl.
 16. The composition of claim 4 in which y 0 and X Br;Hg2P3Br.
 17. The composition of claim 4 in which y 0 and X is 0.5 Br and0.5 Cl; Hg2P3Br0.5Cl0.5.